Bell's Theorem is a fundamental result in quantum mechanics that demonstrates the incompatibility of local hidden variable theories with the predictions of quantum mechanics. It shows that if quantum mechanics is correct, then particles can be entangled in such a way that the measurement of one particle instantly influences the state of another, regardless of the distance separating them. This theorem was formulated by physicist John Bell in 1964 and has profound implications for our understanding of reality. It challenges classical intuitions about separability and locality, suggesting that the universe may be interconnected in ways that defy traditional explanations.